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PubMed1977

Density, porosity, and structure of dried cell walls isolated from Bacillus megaterium and Saccharomyces cerevisiae.

Helium displacement and nitrogen adsorption techniques were used to determine the density and porosity, respectively, of freeze-dried cell walls isolated from Bacillus megaterium KM and Saccharomyces cerevisiae. The densities were 1.302 and 1.180 g/cm3, respectively, suggesting noncrystalline solids. The porosities were extremely small, indicating that the cell walls had collapsed and become essentially impervious upon lyophilization.

Bacillus megaterium↗
PubMed1984

Saccharomyces cerevisiae mannoproteins form an external cell wall layer that determines wall porosity.

A beta-glucanase (Z-glucanase) from Zymolyase was freed from a protease (Z-protease) by affinity chromatography on alpha 2-macroglobulin-Sepharose columns and used to solubilize proteins from isolated cell walls of Saccharomyces cerevisiae. The cell wall proteins were labeled with 125I and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The bulk of the labeled material had very low mobility. Its mannoprotein nature was demonstrated by precipitation with specific antibodies and by conversion to a band with an average molecular weight of 94,000 after incubation with endo-beta-N-acetylglucosaminidase. The intact mannoproteins were hydrolyzed by Z-protease, but were resistant to the enzyme when the carbohydrate was first removed by endo-beta-N-acetylglucosaminidase. In intact cells, lysis of cell walls by Z-glucanase required a previous incubation with z-protease, which led to solubilization of most of the 125I-labeled proteins. Other proteases that did not attack the cell wall mannoproteins were unable to substitute for Z-protease. The specific effect of Z-protease is consistent with the notion that mannoproteins form a surface layer of the cell wall that penetrates the wall to some depth and shields glucans from attack by Z-glucanase. Mannoproteins, however, do not appear to cover the inner face of the cell wall, because isolated cell walls, in contrast to intact cells, were completely solubilized by Z-glucanase in the absence of protease. The function of mannoproteins in determining cell wall porosity was highlighted by the finding that horseradish peroxidase (Mr, 40,000) causes lysis of cells that had been treated with Z-protease. Depletion of mannoproteins by Z-protease also resulted in the disappearance of a darkly stained surface layer of the cell wall, as observed by electron microscopy. Other agents that facilitate cell lysis by Z-glucanase, such as 2-mercaptoethanol, digitonin, and high concentrations of salts, caused little or no solubilization of mannoprotein. We assume that they perturb and loosen the structure of the mannoprotein network, thereby increasing its porosity. The implications of our results for the construction of the yeast cell wall and the anchoring of mannoprotein to the cell are discussed.

Cell Wall↗
PubMed1981

Correlation between macroscopic porosity location and liquid metal pressure in centrifugal casting technique.

Radiographic analysis of uniform cylindrical castings fabricated by the centrifugal casting technique has revealed that the macroscopic porosity is dependent on the location of the sprue attachment to the casting. This is attributed to the significant pressure gradient associated with the centrifugal casting technique. The pressure gradient results in different heat transfer rates at portions of the castings near and away from the free surface of the button. Consequently, the macroscopic porosity is invariably at portions of the casting close to the free surface of the button. In addition, some optimized sprue-reservoir combinations could be predicted and proved, based on this pressure gradient concept.

Chemical Phenomena↗
PubMedDate not supplied

Radiographically detectable intracortical porosity. The dimensions and frequencies of its components in hand bones of normal men and women.

Since the measurement of intracortical resorptive spaces by histologic methods is difficult and very few data are available in normal humans, we have measured their lengths and widths and calculated the intracortical porosity in metacarpals and phalanges of 79 normal women and 69 normal men, using fine-detail radiographs of the hands and a computerized semi-automatic image analysis system (Zeiss MOP-3), this being the first study of this kind. Several methodological problems were solved satisfactorily, and the results of this study could serve as a data bank for further investigations concerned with intracortical resorption. Significant differences were found between age and sex versus several intracortical resorptive parameters; also significant correlations were found with age in some cases. Normal intracortical porosity was found to be about three times greater in the proximal phalanges than in the metacarpals. It is concluded that this methodology could be used for further studies of intracortical resorption in osteoporosis and other metabolic bone diseases.

Adult↗
PubMed1999

Porosity of the epithelial basement membrane as an indicator of macrophage-enterocyte interaction in the intestinal mucosa.

The epithelial basement membrane of intestinal villi is perforated with numerous small pores, through which free cells in the lamina propria communicate with the enterocytes. This study was a comparative analysis of the pores in the basement membrane by SEM after removal of the gut epithelium with OsO4 maceration. The porosity as represented by the area fraction of the pores varied along the baso-apical axis of villi in patterns specific for each animal species examined: consistent scantiness along the entire length of villi in mice, acute elevation in the second and third distal one-sixths of villi in rats, and gradual augmentation toward the villus tips in guinea pigs. Size distribution analyses of the pores indicated their heterogeneous enlargement in the regions of elevated porosity. Concomitant observation of lamina propria macrophages by histochemical labelings and by conventional TEM showed that the cells specifically clustered beneath the hyperporous basement membrane, with their thick processes penetrating it. The spatially-regulated patterns of perforation of the epithelial basement membrane indicate phase-specific interventions of lamina propria macrophages in the maturation or aging of enterocytes, which steadily proliferate in crypts and exfoliate at the villus tips.

Animals↗
PubMed1978

Porosity of resin filling materials.

Four paste-paste types of resin filling materials and three capsulated products were tested with respect to porosity content and size distribution of the pores. The data were obtained by using an automatic image analyzer. The paste-paste products were inserted into the test cavities by a bulk-packing technique and an injection technique. The results showed that the use of a syringe reduced the porosity content, mainly by the elimination of big pores. The capsulated products were not less porous than the paste-paste materials.

Dental Materials↗
PubMed1982

Surface roughness and porosity of dental amalgam.

The surface roughness of seven different products of dental amalgam was determined and the contribution of their porosity content and alloy particle size to that surface property was assessed. A significant correlation between roughness and porosity was found. In all amalgams the small voids were the most frequent. It was also found that the amalgam products which exhibited the highest frequency of big voids presented significantly higher surface roughness values. No significant correlation was found between roughness and alloy particle size.

Dental Alloys↗
PubMedDate not supplied

Polymers for biodegradable medical devices. X. Microencapsulation studies: control of poly-hydroxybutyrate-hydroxyvalerate microcapsules porosity via polycaprolactone blending.

Reservoir-type microcapsules were prepared using a double emulsion solvent evaporation process from a range of different poly-beta-hydroxybutyrate homopolymers and copolymers thereof with 3-hydroxyvalerate (P(HB-HV) polymers) blended with 20 per cent by weight of poly-epsilon-caprolactone (PCL). Microcapsules prepared from these P(HB-HV)/20 per cent PCL blends had very different typical surface morphologies from those prepared from the corresponding unblended P(HB-HV) polymers. At this blend ratio the effects of polymer blending on particle morphology were clearly dependent on the molecular weight of P(HB-HV) polymer and, to a reduced extent, the 3-hydroxyvalerate content. Microcapsules were also prepared from blends of a high molecular weight P(HB-HV) polymer with PCL in which the proportion of the latter was varied from 0 to 100 per cent at 10 per cent intervals. Increasing the proportion of PCL from 0 to 50 per cent produced a systematic and dramatic increase in microcapsule porosity; with only skeletal particles being generated from the even 50-50 blend. When the proportion of PCL in the blends was increased from 50 to 70 per cent the level of particle porosity diminished, and at 80 per cent or above the microcapsules were essentially smooth and non-porous.

Biodegradation, Environmental↗
PubMed1987

High vacuum as a method of reducing porosity of polymethylmethacrylate.

In total hip arthroplasty, fracture and subsequent premature loosening are directly related to the strength of the cement mantle serving as an interface between bone and prosthesis. The cement has been shown to be weakened by its porosity, which enhances the formation of microfractures that contribute to crack propagation. By means of a vacuum mixing method for preparing the cement, nearly all the porosity can be removed and cement strength enhanced by about 17%.

Biomechanical Phenomena↗
PubMed1982

Dacron arterial grafts: the influence of porosity, velour, and maturity on thrombogenicity.

It has been claimed that the neointimal healing of Dacron arterial prostheses can be enhanced by increasing porosity and including both an internal and an external velour layer. To test this, 24 patients received at random either woven (USCI, DeBakey, C. R. Bard, Inc.) or more porous, double-velour, knitted (Microvel, Meadox Medicals, Inc.) Dacron aortobifemoral prostheses. Graft thrombogenicity was measured using autogenous 111In-labeled platelets shortly following surgery and 6 to 9 months later. The thrombogenicity index was defined as the mean daily rise in the ratio of emissions over the graft to emissions over a reference area (aortic arch) and is a measure of platelet deposition. At early study the mean (+/- SE) thrombogenicity index was similar in woven and knitted graft patients at 0.19 +/- 0.4 and 0.14 +/- 0.2, respectively. In both groups it was lower (P less than 0.05) 6 to 9 months later at 0.06 +/- 0.2 (woven( and 0.08 +/- 0.1 (knitted), with again no difference between materials. Although platelet survival was restored to near normal values in both groups by 6 to 9 months, only one woven graft failed to demonstrate continued platelet accumulation by gamma-imaging. Thrombogenicity in Dacron grafts diminishes in the early months of maturation but is not affected by porosity and velour. Moreover, this thrombogenicity persists beyond the period of altered platelet survival.

Aorta, Abdominal↗
PubMed1995

[A case report of Cabrol procedure with zero-porosity graft in a patient of annulo-aortic ectasia with severe aortic regurgitation].

A 63-year-old man was admitted to the hospital for the treatment of annulo-aortic ectasia with severe aortic regurgitation. The aortogram revealed dilatation of the aortic root and severe aortic regurgitation. LVEDVI was 207 ml/m2 but the patient was asymptomatic. Aortic root reconstruction was performed with Cabrol procedure using zero-porosity graft. There was no evidence of bleeding due to this graft and the percent dilatation of this graft was 33%. This zero-porosity graft of knitted Dacron coated with gelatin seems to offer some advantages to the operation. The patient is in stable health today, but perioperative occurrence of VPCs may have owed to diminished LV function caused by severe aortic regurgitation.

Aorta, Thoracic↗
PubMed1994

Autologous fibrin glue for sealing vascular prostheses of high porosity.

Thirty high-porosity double-Velour vascular prostheses were sealed with fibrin glue, the fibrinogen in the glue being prepared from citrated plasma by ethanol precipitation. After such preparation the prostheses were blood-tight at a pressure > 300 mmHg. Using a fibrin concentration of 13 mg/ml (obtained by dilution of the fibrinogen solution) the prostheses were blood-tight at a minimum pressure of 150 mmHg, which is suitable for clinical use. Sufficient fibrin glue can be prepared from 44-88 ml of the patient's blood to seal most types of high-porosity vascular prosthesis used clinically. The fibrin-sealed grafts have good handling characteristics because they are soft, pliable and non-sticky. The use of autologous fibrin glue has obvious safety advantages by preventing both transmission of viral diseases and immunological reactions.

Biomechanical Phenomena↗
PubMed1993

Packing with high-porosity hydroxyapatite cubes alone for the treatment of simple bone cyst.

In 23 patients, simple bone cysts were treated by curettage followed by packing the cavity with cubes of high-porosity hydroxyapatite (HA). In 22 patients, HA was packed exclusively without autogeneic bone graft. Except in one patient who sustained pathologic fracture at the femoral diaphysis, HA was packed with a fibula strut graft. Each case had an uneventful postoperative course and was followed, on average, two years. Complete healing without cyst recurrence occurred in 18 cases (78%). In three cases--all rapidly growing children--a new cyst appeared between the epiphyseal plate and the HA packing, but the original cysts did not recur. In two multiloculated cysts, the cavities were not filled fully and healing was incomplete, yet there was no cyst recurrence. In the entire group, new bone surrounding HA was roentgenographically evident within an average of 2.3 months. Thus, the result of packing high-porosity HA for simple bone cysts compares favorably with the cure rates reported either with autogeneic bone graft, or topical steroid injection.

Adolescent↗
PubMed1996

[Perforations and porosity of surgical gloves. Frequency, mechanism, risk].

Surgical gloves constitute part of the most exposed barrier material, as one half of accidental exposures to blood in the exposures to blood in the operating room involve the hands. Approximately 15% of gloves tested at the end of the operation were found to be perforated. Double gloving lowers this rate to 5% with apparently acceptable tolerance for surgeons. Although surgical glove are initially impermeable to various viruses, the porosity increases with the duration of use. This porosity is related to hydratation and deformation of latex fibres. The maintenance of a good barrier function of surgical gloves requires regular changing, at least hourly, in the current state of knowledge.

Acquired Immunodeficiency Syndrome↗
PubMed1997

The effects of porosity on endothelialization of ePTFE implanted in subcutaneous and adipose tissue.

Healing of biomaterial implants varies depending on the type and structure of material and the tissue surrounding the implant. In this study we examined structural differences of 30 microm, 60 microm, and 100 microm expanded polytetrafluoroethylene (ePTFE) using scanning electron microscopy, and we also investigated differences in healing for these three different porosity ePTFE grafts implanted within subcutaneous tissue and adipose tissue. Scanning electron microscopic examination of 30 microm, 60 microm, and 100 microm ePTFE revealed structural differences and differences in fiber density within the internodal space. Circular patches (6 mm in diameter) of 30 microm ePTFE were implanted within subcutaneous tissue and epididymal fat pads of male Sprague-Dawley rats. After 5 weeks, the implants were removed and analyzed for fibrous capsule formation, endothelialization, and for activated monocytes and macrophages in association with the material. Histological evaluation revealed dense fibrous capsule formation surrounding only the 30 microm ePTFE subcutaneous implants. From immunohistochemistry data obtained, we generated an Endothelialization Index (measure of neovascularization) and a Monocyte/Macrophage Index (measure of inflammatory response) for each sample. Consistently, 60 microm ePTFE had the greatest Endothelialization Index at both implant sites while 100 microm ePTFE generally had the largest values for the Monocyte/Macrophage Index. These data indicate that both the structure of the material and the site of implant influence the healing characteristics of ePTFE and suggest that activated monocytes and/or macrophages associated with the implant may inhibit endothelialization of ePTFE.

Adipose Tissue↗
PubMed1999

Effect of porosity and environment on the mechanical behavior of acrylic bone cement modified with acrylonitrile-butadiene-styrene particles: I. Fracture toughness.

The elastomeric copolymer acrylonitrile-butadiene-styrene (ABS) was added to a conventional acrylic bone cement matrix. The results obtained show that although strength and stiffness decreased with an increasing second phase volume fraction, ductility and toughness both increased. The crack propagation became stable for specimens containing over a 5% volume fraction of the second phase. The fracture toughness increased up to 60% when the amount of ABS reached 20% (v/v). For larger amounts linear elastic fracture mechanics techniques could not be used properly. The effects of porosity and environmental conditions on the mechanical behavior were also studied. The mechanisms that control the fracture process were investigated by means of scanning electron microscopy.

Acrylic Resins↗
PubMed2001

Strong and macroporous calcium phosphate cement: Effects of porosity and fiber reinforcement on mechanical properties.

Because of its excellent osteoconductivity and bone-replacement capability, self-setting calcium phosphate cement (CPC) has been used in a number of clinical procedures. For more rapid resorption and concomitant osseointegration, methods were desired to build macropores into CPC; however, this decreased its mechanical properties. The aims of this study, therefore, were to use fibers to strengthen macroporous CPC and to investigate the effects of the pore volume fraction on its mechanical properties. Water-soluble mannitol crystals were incorporated into CPC paste; the set CPC was then immersed in water to dissolve mannitol, producing macropores. Mannitol/(mannitol + CPC powder) mass fractions of 0, 10, 20, 30, and 40% were used. An aramid fiber volume fraction of 6% was incorporated into the CPC-mannitol specimens, which were set in 3 mm x 4 mm x 25 mm molds and then fractured in three-point flexure to measure the strength, work of fracture, and modulus. The dissolution of mannitol created well-formed macropores, with CPC at 40% mannitol having a total porosity of a 70.8% volume fraction. Increasing the mannitol content significantly decreased the properties of CPC without fibers (analysis of variance; p < 0.001). The strength (mean +/- standard deviation; n = 6) of CPC at 0% mannitol was 15.0 +/- 1.8 MPa; at 40% mannitol, it decreased to 1.4 +/- 0.4 MPa. Fiber reinforcement improved the properties, with the strength increasing threefold at 0% mannitol, sevenfold at 30% mannitol, and nearly fourfold at 40% mannitol. The work of fracture increased by 2 orders of magnitude, but the modulus was not changed as a result of fiber reinforcement. A scanning electron microscopy examination of specimens indicated crack deflection and bridging by fibers, matrix multiple cracking, and frictional pullout of fibers as the reinforcement mechanisms. Macroporous CPCs were substantially strengthened and toughened via fiber reinforcement. This may help extend the use of CPCs with macropores for bony ingrowth to the repair of larger defects in stress-bearing locations.

Algorithms↗
PubMed2006

Room temperature synthesis of agarose/sol-gel glass pieces with tailored interconnected porosity.

An original shaping technique has been applied to prepare porous bodies at room temperature. Agarose, a biodegradable polysaccharide, was added as binder of a sol-gel glass in powder form, yielding an easy to mold paste. Interconnected tailored porous bodies can be straightforwardly prepared by pouring the slurry into a polymeric scaffold, previously designed by stereolitography, which is subsequently eliminated by alkaline dissolution at room temperature. The so obtained pieces behave like a hydrogel with an enhanced consistency that makes them machinable and easy to manipulate. These materials generate an apatite-like layer when immersed in a simulated body fluid, indicating a potential in vivo bioactivity. The proposed method can be applied to different powdered materials to produce pieces, at room temperature, with various shapes and sizes and with tailored interconnected porosity.

Biocompatible Materials↗